Net Income Per Common Share (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Earnings Per Share Disclosure [Line Items]
Net Income	$ 216.4	$ 227.6	$ 430.3	$ 451.2
Denominator (000s)
Weighted Average Common Shares - Basic	283,316,600	306,316,200	286,874,500	309,513,000
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	424,000	1,094,800	639,300	1,342,400
Weighted Average Common Shares - Assuming Dilution	283,740,600	307,411,000	287,513,800	310,855,400
Net Income Per Common Share
Basic	$ 0.76	$ 0.74	$ 1.50	$ 1.46
Assuming Dilution	$ 0.76	$ 0.74	$ 1.50	$ 1.45